Prevent your fish from being sucked up during water changes and prevent gravel and sand from being disturbed when filling tank back up. Simply slides over end of siphon tube. Designed for Python, Aqueon, and Topfin gravel vacuum tubes, however they may fit other brands. The different variations have different diameters that fit different models of siphon tubes. If you are unsure which one is best for you please reach out! Feel free to contact us with any questions!